1. Field of the Invention
The present invention relates to forming a seam in the body outer panel of a vehicle such as an automobile. 2. Description of the Prior Art
The body outer panel of a vehicle such as an automobile is usually constructed of a plurality of plate elements which have been preformed by a press, said elements being joined with each other thereby forming a seam at the joining portion. For example, as shown in FIG. 1, the side wall portions of an automobile provided at the opposite sides of a rear window 1 include seams 4 formed between a roof panel 2 and quarter panels 3. These seams should preferably be formed so as not to be noticable from the outside. For this purpose, the seam 4 is conventionally formed by the procedures as shown in FIG. 2. Explaining in detail, the rear quarter panel 3 is largely bent inwardly at a seam forming location to provide a recess portion 3a, while the roof panel 2 is also largely bent inwardly at a seam forming location to provide a bent portion 2a. The bent portions 2a and 3a are joined together by spot welding so as to form co-welded portions 5. Then a recess 6 defined by the bent portions 2a and 3a is filled with a lump of solder having an outer surface 8 which swells beyond a smooth transient contour surface 7 connecting the roof panel 2 and the rear quarter panel 3. After the solder has solidified, an excessive portion thereof is removed by a grinding process until the seam 4 having the smooth contour surface 7 is obtained. The conventional method of mounding a lump of solder presents an occupational disease situtation in that the worker's health can be injured by the atmosphere produced by soldering. With regard to the quality of this product, the conventional method is not advantageous because the quality rapidly deteriorates by generation of pinholes or blisters making it difficult to obtain a good finish of the painted surface. Furthermore, the conventional method has an economical disadvantage because it requires a large amount of manpower and materials. In order to avoid the soldering process, to connect joining ends of the roof panel 2 and the rear quarter panel 3 individually formed to follow the final panel contour, other techniques such as fusion welding, pressure welding, brazing or the like have been attempted. These techniques employ a substantially larger quantity of heat which is charged to the joining portion relative to the heat employed in the soldering process thereby causing a problem in that the thin plates such as those forming the outer panel of automobile are deformed. This deformation produces a waving of the panels running along the welding line and causes deflections perpendicular to the welding line, making it extremely difficult to amend the deformation.